This invention relates to a catalyst and process for preparing amines from alcohols, aldehydes or cautions.
It is well-known to prepare amines from alcohols, aldehydes and cautions by the reductive amination thereof using ammonia and hydrogen. These processes are typically conducted in the presence of various metallic catalysts, as described, for example, in U.S. Pat. Nos. 3,151,113; 3,347,926; 4,036,883; and 3,654,370. In these processes, the alcohol, aldehyde or ketone is contacted with ammonia and hydrogen under elevated temperatures and pressures to convert the alcohol, aldehyde or ketone group to a primary amine group.
A wide variety of alcohols can be converted to amine using this process. For example, low molecular weight alcohols such as 2-methylbuten-1-ol-4 and diethylene glycol have been converted to the primary amines using a reductive amination (ammonolysis) process. Similarly, polyether polyols have been converted to primary amine-terminated polyethers in this manner.
The last mentioned amine-terminated polyethers have been found to be useful in preparing urea-modified polyurethanes and molded polyureas. See, e.g., U.S. Pat. Nos. 4,444,910 and 4,269,945. While their use in these applications has provided polymers with various desirable properties, notably improved stiffness and high temperature properties, these amine-terminated polyethers are so reactive that it is sometimes difficult to process them even on high pressure reaction injection molding equipment. Accordingly, their use in making polyurea polymers has been very limited.
One method to reduce the reactivity of the amine-terminated polyethers is to introduce stearic hindrance by converting the primary amine group to a secondary amine group. Methods for accomplishing this include reacting the primary amine-terminated polyether with an unsaturated compound like acrylonitrile in a Michael addition reaction to form terminal --NH(CH.sub.2 CH.sub.2 CN) groups, or alkylating the primary amine. However, these methods involve an additional processing step, which increases their cost of manufacture significantly. In addition, these methods provide mixtures of products.
It would be more desirable to prepare the secondary amine-terminated polyether directly from the corresponding polyol by amination with a primary amine. However, this method has not been successful to date because with the use of previously known catalysts a large number of side reactions occur. The product therefore contains large quantities of undesired primary amine groups and some tertiary amines, as well as the desired secondary amine groups and a significant amount of residual hydroxyl groups. The problem is compounded since the species with differing terminal groups cannot be separated by any practical method.
Accordingly, it would be desirable to provide a method whereby alcohols, aldehydes or cautions are converted to amines more efficiently than previous methods. In particular, it is desirable to provide an efficient process for the amination of alcohols, aldehydes or cautions with a primary amine, whereby a secondary amine is obtained in good yield with reduced amounts of undesired by-products. In addition, it is desirable to provide a novel catalyst which provides for an improved amination process.